STLC60134 datasheet(7/22 Pages) STMICROELECTRONICS

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RX PATH

Speech filter

An external bi-directional LC filter for up and

downstream POTS service splits the speech sig-

nal from the ADSL signal to the POTS circuits on

ATU-C.

The ADSL analog front end integrated circuit

does not contain any circuitry for the POTS serv-

ice but it guarantees that bandwidth is not dis-

turbed by spurious signals from the ADSL-spec-

trum.

Channel Filters

The external analog circuits provide partial echo

cancellation by an analog filtering of the receive

signal for both ATU-R (Reception of downstream

channel) and ATU-C (Reception of upstream

channel). This is feasible because the upstream

and the downstream data can be modulated on

separate carriers (FDM).

Line Noise Model

The power spectral density of the crosstalk noise

sources as described in ANSI document is given

in the figure below (no HDB3 interferer signals).

Also given in dotted line, is the noise model used

in this document to specify the sensivity require-

ments which are stronger than the original ones.

Signal to Noise Performance

RX- PATH SENSITIVITY AT MAXIMUM GAIN

The RX path sensitivity at the maximal RX-AGC

of the ATU-R receiver is defined at -140dBm/Hz

(for 100

Ω ref) on the line. This figure corresponds

to the equivalent input noise of 31nVHz-1/2 seen

on the line.

The sensitivity at the maximal RX - gain of the

ATU-C receiver is defined at -130dBm/Hz (for

100

Ω ref) on the line. The figure corresponds to

the equivalent input noise of 100n VHz-1/2 seen

on the line.

Both noise figures include the noise of the hybrid.

It is the equivalent average thermal noise over

the frequency band of

interest. The maximum

noise density within the pass band can exceed

the average value as follows:

ATU-R RX path (max AGC setting):

<100nVHz-1/2 @ 138kHz

<31nVHz-1/2 for 250kHz < f

ATU-C RX path (max AGC setting):

<100nVHz-1/2 for 34.5kHz < f <138kHz

RX-PATH NOISE AT MINIMUM GAIN

At the minimum AGC the total average thermal

noise of the analog RX-path at the ADC input

should be lower than the ADC quantisation noise.

The maximum noise density within the pass band

can exceed the average value as follows:

ATU-R RX path (min AGC setting):

<500nVHz-1/2 @ 138kHz < f

ATU-C RX path (min AGC setting):

<1.5

µVHz-1/2 @ 34.5kHz < f < 138kHz

These noise specifications correspond with 10bit

resolution of the complete RX-path.

Table 4. RX Common-mode Voltage

Description

Value/Unit

Common mode signal VCM

at RXIN1 and RXIN2:

1.6V < VCM <1.7V

AGC of RX path

The AGC gain in the RX-path is controlled

through a 5-bits digital code.

Four inputs are provided for RX input and the se-

lection is made with the RXMUX bits of the

CTRLIN interface. This can be used to make

lower gain paths in case of high input signal.

Table 5. AGC Characteristics.

Description

Value/Unit

Input referred noise

(max. gain)

20nVHz

-1/2

Max. input level

1Vpd

Max. output level

1Vpd

Gain range

0 to 31dB with step = 1dB

Gain and step accuracy

± 0.3dB

RX Filters

The combination of the external filter (an LC lad-

der filter typically) with the integrated lowpass fil-

ter must provide:

- echo reduction to improve dynamic range

- DMT sidelobe and out of band (anti-aliasing)

attenuation.

- Anti alias filter (60dB rejection @ image freq.)

79.5 138

250

795

kHz

D98TL359

-140

-130

-120

-110

-100

dBm/Hz

Figure 6. Crosstalk PSD.

STLC60134S

7/22

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